Arc ion plating is known as a method for forming a film on a work. In the arc ion plating, vacuum arc discharge is performed in a vacuum atmosphere using a target as a cathode, the target being formed of a material to be evaporated for forming a film. This discharge causes the target material to be evaporated and ionized. The resulting target material ions are conducted to a work and form a film on the work. For forming a hard film of a metal nitride or a metal carbide by the arc ion plating there is performed reactive coating in which a reactive gas is introduced into a vacuum chamber, e.g., such reactive coating as introducing N2 gas to a target formed of Cr to form a CrN film.
As an example of a conventional arc ion plating method there is disclosed in Patent Literature 1 an arc ion plating method (a vacuum arc evaporation method) using a cylindrical rod target whose both longitudinal end portions are formed thicker than its central portion. This conventional arc ion plating method will now be described with reference to FIGS. 7 to 10. FIG. 7 is a schematic configuration diagram of an apparatus for carrying out the conventional arc ion plating method, FIG. 8 is a front view of a rod target shown in FIG. 7, FIG. 9 is a sectional front view of the rod target and FIG. 10 is a diagram for explaining how to produce the rod target.
In FIG. 7, a rod target 52 and a work 53 are disposed within a vacuum chamber 51 in a state in which the respective longitudinal axes are parallel or nearly parallel to each other. The rod target 52 is in the form of a cylinder having intermediate stepped portions and is disposed at the center of the chamber 51 in a upright attitude extending vertically.
A rotary table 55 is disposed in a lower portion of the vacuum chamber 51 and it is supported rotatably about a vertical axis which is approximately coincident with the axis of the rod target 52. The work 53 which extends vertically is placed upright on the rotary table 55 through a holding member 56. With rotation of the rotary table 55, the work 53 rotates around the rod target 52 and also rotates about a vertical axis of the work 53 together with the holding member 56. A magnet 54 is disposed within the rod target 52 in a vertically movable manner.
This apparatus is further provided with an arc power supply 57 having an anode and a cathode. The cathode is connected to an upper end of the rod target 52 and the anode is connected to the vacuum chamber 51. That is, the rod target 52 is set to the cathode and the vacuum chamber 51 is set to the anode.
As shown in FIGS. 8 and 9, the rod target 52 has a shape such that both longitudinal end portions thereof are thicker than its central portion. That is, both longitudinal end portions of the rod target 52 are large-diameter portions (thick portions) 521, 521, while a central portion thereof is a small-diameter portion (thin portion) 522.
For fabricating the rod target 52 there is used HIP treatment wherein the powder of a target material is pressed by HIP (hot isostatic pressing). More particularly, as shown in FIG. 10, the rod target 52 is fabricated by a method comprising a step of forming the large-diameter portions 521, 521 and small-diameter portion 522 each individually into simple cylindrical shapes by the HIP treatment and a step of assembling them so that the large-diameter portions 521, 521 and the small-diameter portion 522 are united.
In this conventional arc ion plating method, the target 52 and the work 53 are disposed in a state in which the respective longitudinal axes are parallel or nearly parallel to each other, and target material ions are conducted to the work 53 by vacuum arc discharge using the target 52 as a cathode to form a film on the surface of the work. As the target 52 there is used one having the large-diameter portions 521, 521 as both longitudinal end portions and the small-diameter portion 522 as a central portion and the position of an arc spot on the target surface is controlled by a vertical movement of the magnet 54. With this control, the formation of a film on the work 53 is promoted while making the consuming speed of the large-diameter portions 521, 521 higher than that of the small-diameter portion 522, thereby making it possible to obtain a uniform film thickness distribution such that variations in film thickness is within ±5% substantially throughout the overall length of the work 53.
If the target consuming speed (target material evaporation quantity) is uniform in the longitudinal direction of the target, the area ensuring a uniform film thickness in the work 53 is limited to the center and the vicinity thereof of the work. Thus, for obtaining a uniform film thickness substantially throughout the overall length of the work it is necessary to increase the consuming speed at both end portions of the target.
Accordingly, in the conventional arc ion plating method in question there is used the rod target 52 whose both longitudinal end portions are formed thicker than its central portion to correspond to the foregoing consuming speed distribution considered necessary for attaining a uniform film thickness. The rod target 52 of such a shape is high in utilization efficiency as compared with a cylindrical target free of stepped portions and there is no waste of the target material.
However, the conventional arc ion plating method described above is disadvantageous in that the production efficiency of the rod target 52 is poor. More particularly, the shape of the rod target 52 is restricted to such a special shape as its both longitudinal end portions being thicker than its central portion. This makes the manufacturing process for the rod target 52 complicated. Besides, a demand exists for a further reduction of the target cost.                Patent Literature 1: Japanese Patent Laid-Open Publication No. 2004-107750 (FIGS. 1 to 3 and 9)        Patent Literature 2: Japanese Patent Laid-Open Publication No. 2003-301266 (FIG. 1)        